During the Mesozoic Era, dinosaurs ruled the land, but their flying cousins the pterosaurs ruled the sky. They first appeared during the late Triassic Period about 210 million years ago, and persisted until the reign of the reptiles came to an end 66 million years ago.
For pterosaurs, the middle of the Cretaceous Period, approximately 120-90 MYA, was their golden age. More species were alive at one time during this stage of their overall existence than at any other. South America, and especially Brazil, appears to have been a place where these magnificent flying reptiles existed in glorious splendor, as plentiful and diverse as tropical birds are today.
Unfortunately, in contrast to the abundance of fossils from South America, there aren’t many pterosaur fossils from the middle Cretaceous which have been found in North America. The total number which has been uncovered here amounts to only a handful of specimens, and all of them are fragmentary. These isolated bones give us tantalizing glimpses to what must have been a great diversity of species, but alas, these fleeting glimpses are all we presently have.
In 1977, a single left humerus from a pterosaur (collection ID code: SMU 72547) was discovered by Vernon Mills during the construction of an emergency spillway for the Comanche Peak nuclear power plant, which is located approximately 4.5 miles north of the town of Glen Rose, Texas (a place famous in paleontology for the fossil footprint trackways which were likely made by the dinosaurs Acrocanthosaurus and Astrodon). The upper arm bone was found within the strata of the appropriately-named Glen Rose Formation, which dates to 113-111 MYA. In addition to the humerus, fossilized plant material and numerous fish bones, scales, and teeth were also recovered nearby. This humerus specimen was first described in 1991. It was stated to belong to a species within the pterosaur family Azhdarchidae. However, the authors of that research paper didn’t venture to ascribe a name to this specimen (Murry et al. 1991, pages 167-170). Then in 2013, this fossil was redescribed, and it was given the name Radiodactylus langstoni. The genus name, meaning “radioactive finger”, was in reference to the fact that the fossil was found near a nuclear power plant, and the trend of having pterosaur names ending with –dactylus, even though in this case a finger bone wasn’t found. The species name is given in honor of Texas paleontologist Wann Langston Jr. (1921-2013), who had worked extensively on pterosaur research. This paper stated that Radiodactylus was a member of the pterosaur super-family Azhdarchoidea, but was not within the family Azhdarchidae, as was earlier claimed (Andres and Myers 2013, pages 384, 387).
Additionally, a pterosaur wing bone (collection ID code: TMM 42593-1) was uncovered in Somervell County, Texas within the rocks of the Glen Rose Formation. It is possible that this specimen also belongs to Radiodactylus. However, it’s also possible that this bone belongs to a second pterosaur species which inhabited the area during that time. Isolated bone fragments which were uncovered within north-central Texas were identified as belonging to the family Dsungaripteridae. These were pterosaurs with nutcracker-like jaws which were specially built for cracking open shells. Considering that fossilized shells belonging to five different genera of clams were found within similarly-aged rocks in Wyoming (Bergendahl et al. 1960, page 650), and considering that the Glen Rose Formation had a comparable coastal ecosystem, then it’s very likely that there would be an animal of some sort which would take advantage of such an abundant food source. Therefore, having a dsungaripterid pterosaur flying around North America circa 112 MYA would not be unreasonable, and thus the wing bone TMM 42593-1 cannot be definitively stated to be another bone from Radiodactylus (Andres and Myers 2013, pages 384, 387, 390).
Determining how Radiodactylus looked is problematic due to the scarcity of remains. A paper published in 2018 stated that Radiodactylus‘ closest relative was the genus Eoazhdarcho, which lived in China around 120 MYA (Longrich et al. 2018: e2001663), and therefore the two probably looked similar. Preserved skulls from related pterosaur genera show that the early azhdarchoideans within the families Azhdarchidae and Chaoyangopteridae has tweezer-like or forceps-like jaws with a low S-shaped curvature. Radiodactylus probably had a skull like this. The skull shape looks similar to that of the famous pterosaur Pteranodon, and indeed, the pteranodontids and the azhdarchoideans are not too distantly related to each other. Would Radiodactylus have had a crest? Perhaps. Late derived azhdarchids possessed elongated cylindrical neck vertebrae – long neck, but reduced flexibility. However, early azhdarchids like the Chinese genus Eoazhdarcho had shorter neck vertebrae seen in other pterosaurs. Many derived azhdarchid pterosaurs had a short wingspan and small wing area in relation to overall body size. This has led some people to suspect that the azhdarchids, especially the very large genera such as Quetzalcoatlus and Hatzegopterus, were too big and heavy to fly and lived a terrestrial lifestyle, and their wings were steadily becoming vestigial. However, the genus Eoazhdarcho, which is a primitive member of this group and which Radiodactylus is closely related to, had a large wingspan similar to that seen in many other pterosaurs. This appears to be further evidence that as the azhdarchids got bigger, their wingspans got proportionally shorter. However, the debate on whether or not the large azhdarchids could fly is a lengthy and contentious one which cannot be delved into here.
Radiodactylus shared its environment with other creatures who called the Gulf Coast of Texas home during the middle of the Cretaceous Period including the 35 foot long theropod Acrocanthosaurus, the 90 foot long sauropod Sauroposeidon, the 20 foot long ornithopod Tenontosaurus, turtles, and numerous species of freshwater and saltwater fish (Barck 1992, pages 3-24).
Below is an illustration of what Radiodactylus might have looked like. The drawing was made with No.2 pencil and colored pencils on printer paper, followed by substantial computer touch-up.
Radiodactylus. © Jason R. Abdale (November 29, 2023).
UPDATE (February 28, 2024):
Finger bones belonging to a pterosaur of some sort have also been found within the Antlers Formation of north-central Texas, dated to the Aptian and Albian Stages of the middle Cretaceous Period. These had been discovered in 1950, and were afterwards noted to be similar in appearance to those belonging to the Asian genus Dsungaripterus, although most papers merely listed them as “Pterosauria indet.”, meaning “species unknown”. In February 2024, these bones were ascribed to the family Tapejaridae, which is within the super-family Azhdarchoidea (Bennett 2024). It’s possible that these phalanges also may belong to Radiodactylus, but this cannot be proven at this point.
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Bibliography
Andres, Brian; Myers, Timothy S. (2013). “Lone Star Pterosaurs”. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, volume 103, issue 3-4. Pages 383-398.
https://www.researchgate.net/publication/259437218_Lone_Star_Pterosaurs.
Barck, Alan (1992). “Paleontology of the Glen Rose Formation (Lower Cretaceous) Hood County, Texas”. The Texas Journal of Science, volume 44, issue 1 (February 2, 1992). Pages 3-24.
https://www.thefreelibrary.com/Paleontology+of+the+Glen+Rose+Formation+(Lower+Cretaceous)%2C+Hood…-a0128663802.
Bennett, S. C. (2024). “Wing phalanges of a ?thalassodromine pterosaur from the Aptian–Albian Antlers Formation of Texas, USA”. Cretaceous Research, volume 154 (February 2024): 105771.
https://www.sciencedirect.com/science/article/abs/pii/S0195667123002999.
Bergendahl, M. H.; Davis, R. E.; Izett, G. A. (1960). “Geology and Mineral Deposits of the Carlisle Quadrangle, Crook County, Wyoming”. U. S. Department of the Interior Geological Survey Bulletin 1082-I: Geology and Mineral Deposits of the St. Regis-Superior Area, Mineral County, Montana. Washington: United States Government Printing Office, 1960. Pages 613-706.
https://books.google.com/books?id=N6YPAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false.
Longrich, Nicholas R.; Martill, David M.; Andres, Brian; Penny, David (2018). “Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary”. PLOS Biology, volume 16, issue 3: e2001663 (March 13, 2018).
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2001663.
Murry, Philip A.; Winkler, Dale A.; Jacobs, Louis L. (1991). “An azhdarchid pterosaur humerus from the Lower Cretaceous Glen Rose Formation of Texas”. Journal of Paleontology, volume 65, issue 1 (January 1991). Pages 167-170.
Categories: Paleontology, Uncategorized
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